Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review

Abstract

The microcirculation is a major topic in current physiology textbooks and is frequently explained with schematics including the precapillary sphincters and metarterioles. We re-evaluated the validity and applicability of the concepts precapillary sphincters and metarterioles by reviewing the historical context in which they were developed in physiology textbooks. The studies by Zweifach up until the 1950s revealed the unique features of the mesenteric microcirculation, illustrated with impressive schematics of the microcirculation with metarterioles and precapillary sphincters. Fulton, Guyton and other authors introduced or mimicked these schematics in their physiology textbooks as representative of the microcirculation in general. However, morphological and physiological studies have revealed that the microcirculation in the other organs and tissues contains no metarterioles or precapillary sphincters. The metarterioles and precapillary sphincters were not universal components of the microcirculation in general, but unique features of the mesenteric microcirculation.

Microchannel network hydrogel induced ischemic blood perfusion connection

“…The microchannel size (16.37 ± 7.76 µm) and closed 3D network played a crucial role in guiding this regenerative mechanism in the gelatin hydrogel implantation 14,15 . The microchannel size was set up first to mimic the diameter range of capillary (5-10 µm), a small blood vessel 38 . Second, our previous studies proved that this diameter range of pores promoted micro blood vessel formation into the polymer's scaffolds when implanted subcutaneously in mice 39 while also accelerating the histological and functional recoveries of post hepatectomy liver via implantation of the same vascular network hydrogel that also contained minced pieces of autologous liver tissue in rabbits 31 .…”

Skeletal muscle interstitial O2 pressures: bridging the gap between the capillary and myocyte

“…Although undoubtedly laying the foundation for skeletal muscle microcirculatory O 2 transport and developing crucially the importance of diffusive O 2 transport, the Krogh‐Erlang model has been called into question by contemporary theoretical and experimental evidence. Several of its assumptions, including the notion of “capillary recruitment” during the rest‐contraction transient, have been theoretically and empirically challenged . Modern tools and techniques not subject to the manifest problems of early microcirculatory preparations (eg, carbon particle aggregation or supra‐physiological perfusion pressures as described below) have allowed a closer inspection of the microvascular network and advanced significantly our understanding of the O 2 transport pathway within skeletal muscle.…”

“…A key facet of the Krogh‐Erlang model lies in the presumption that skeletal muscle capillaries are not passive vessels but, instead, capable of regulating their perfusion via actions of precapillary sphincters and/or the capillary wall itself. At least part of the still‐widespread belief that precapillary sphincters are blood flow and pressure regulators stems from the mistaken view that such structures are universal components of the microcirculation . While reported as a feature of the mesenteric microcirculation in certain species (as originally described via camera lucida illustrations by Benjamin W. Zweifach), unequivocal morphological evidence for the presence of precapillary sphincters within mammalian skeletal muscle is completely absent .…”

“…At least part of the still‐widespread belief that precapillary sphincters are blood flow and pressure regulators stems from the mistaken view that such structures are universal components of the microcirculation . While reported as a feature of the mesenteric microcirculation in certain species (as originally described via camera lucida illustrations by Benjamin W. Zweifach), unequivocal morphological evidence for the presence of precapillary sphincters within mammalian skeletal muscle is completely absent . In addition, it is now well established that bulk blood flow and pressure regulation largely take place at the arteriolar level in the peripheral circulation .…”

Organ Specificity and Functional Relevance of the Arterial Structure: A Comparative Study in the Kidney and the Skeletal Muscle with Electron Microscopy

“…In spite of the extreme functional differences among organs, the structural heterogeneity of minute vessels has been only poorly investigated. Recently, on the basis of a historical survey of the literature, Sakai and Hosoyamada [9] revealed that the well-known structural components of microvasculature, such as precapillary sphincters and meta-arterioles, are not ubiquitous structures but are specific to the microcirculation of the mesenterium.…”